Does anyone happen to have both Rehabilitations and Other Essays and Selected Literary Essays? Both appear to contain the essay "The Alliterative Metre", and I wonder if the essays are identical in both books.

(Was thinking of buying Rehabilitations and Other Essays just to check if it quotes from a Tolkien letter, but the cheapest copy goes for £200.00 at Amazon.co.uk!)

I have a copy of each - Lewis's text is the same in each edition (as far as I can see). There's no mention of a Tolkien letter in 'Rehabilitations' but in 'Selected Essays' Walter Hooper notes that he'd asked Tolkien about Lewis's example of alliterative verse beginning with 'We were talking of dragons, Tolkien and I'.

Tolkien's reply is published here (note 1 on p.18) - a slightly abridged version of Letter no.300 in 'Letters of JRR Tolkien'.